The present invention relates to instruments known as light-responsive electric switches which as a function of the illumination permit of closing or opening one or more circuits for the control of lighting, especially public street lighting, according to the time and the momentary degree of illumination.
These instruments, in order to fulfil their task, namely the obtaining of energy economy, must be extremely reliable, precise and economical, while avoiding any untimely putting into or out of action, that is lighting or extinguishing, of the lighting system in the case of rapid variations of illumination caused for example by the headlights of automobile vehicles or by other instantaneous and/or transient causes.
The apparatus according to the invention permits of solving this problem in a particularly interesting manner, by the fact that it is of simple construction, small bulk and in that it offers numerous possibilities of combinations, by virtue of which multiple automatic systems are realisable.